Humid heatwaves, characterized by high temperature and humidity combinations, challenge tropical societies. Extreme wet-bulb temperatures (TW) over tropical land are coupled to the warmest sea surface temperatures (SST) by atmospheric convection and wave dynamics (see Zhang, Held, and Fueglistaler, 2021 on my publications page for details). Here, we harness this coupling for seasonal forecasts of the annual maximum of daily maximum TWmax. In Zhang et al. (2023), we develop a multiple linear regression model that explains 80% of the variance in tropical mean TWmax and significant regional TWmax variances. Forecast of the annual maximum wet-bulb temperature TWmax averaged over land between 30°S and 30°N and over four regions listed in the menu below. Place your mouse on the interactive chart to read the probability of setting new records. The current Oceanic Niño Index forecast for December 2023 is 2.0 based on IRI (last updated Nov 2023).
Map of the root mean squared error (RMSE) of the model and the four focus regions in red boxes.
References
2023
Forecasting Tropical Annual Maximum Wet-Bulb Temperatures Months in Advance from the Current State of El Niño
Yi Zhang, William R Boos, Isaac Held, and 2 more authors
Human bodies, ecosystems and infrastructures display a non-linear sensibility to extreme temperatures occurring during heatwave events. Preparing for such events entails to know how high surface air temperatures can go. Here we examine the maximal reachable temperatures in Western Europe. Taking the July 2019 record-breaking heatwave as a case study and employing a flow analogues methodology, we find that temperatures exceeding 50 ∘C cannot be ruled out in most urban areas, even under current climate conditions. We analyze changes in the upper bound of surface air temperatures between the past (1940–1980) and present (1981–2021) periods. Our results show that the significant increase in daily maximum temperatures in the present period is only partially explained by the increase of the upper bound. Our results suggest that most of the warming of daily maximum surface temperatures result from strengthened diabatic surface fluxes rather than free troposphere warming.
